The present invention is related to the application entitled A HIGH-FREQUENCY LOW-VOLTAGE MULTIPHASE VOLTAGE-CONTROLLED OSCILLATOR, Ser. No. 09/726,282, which is filed even date hereof, assigned to the same assignee, and incorporated herein by reference.
1. Technical Field
The present invention relates to timing of a signal in a computer system. More specifically, the present invention relates to timing communication signals. Still more specifically, the present invention relates to a system and method for utilizing a multiphase timing device which provides variable phase and frequency.
2. Description of Related Art
A high frequency voltage controlled oscillator (VCO) is extremely important for applications such as processor clock generation and distribution, wired and wireless communication, system synchronization and frequency synthesis. Research on VCOs for the past decade has been concentrated in the areas of raising the frequency, reducing jitter, lowering the operating voltage and power, and increasing the frequency tuning range. Often these design goals are achieved only at the expense of some or all of the other performance objectives.
High frequency analog VCOs operating with current sources may have signal amplitudes that are only a small fraction of the supply voltage, severely limiting their usefulness. Current starved ring oscillators using three or four levels of cascading have become quite common, but they are extremely noise sensitive because of their very high gain, are inherently nonlinear (especially near cutoff where they often stop oscillating), are sensitive to fabrication process and operating environments, and exhibit excessive jitter characteristics. Delay interpolating oscillators are capable of very low jitter due to low gain and low noise sensitivity, but they are inherently limited in frequency range and are difficult to build in less than four levels. Multiphase oscillators offer advantages by pipelining operations using equally spaced phases at lower frequencies, but control mechanisms in delay interpolators introduce offsets from the ideal phase spacing. Inductive-capacitive (LC) oscillators are capable of high frequency and extremely low jitter but are difficult to integrate and model, and also have tuning ranges of only a few percent.
Therefore, it would be advantageous to have a multiphase voltage controlled oscillator with variable phase and frequency.
The present invention provides a voltage controlled oscillator comprising a loop composed of multiple delay elements with amplification in which delay element amplification polarities are connected to sustain oscillation in the loop. Multiple feed forward elements are individually connected in functional parallel with two or more delay elements so that signals transmitted through corresponding delay elements and feed forward elements maintain polarities at element connections to sustain oscillation. Controls within the feed forward elements regulate signal transmission through feed forward elements responsive to one or more control voltages.
In addition, the voltage controlled oscillator includes a selection unit connected to the set of feed forward elements. The selection unit couples the one or more control voltages to selected feed forward elements from within the set of feed forward elements to alter the feed forward path gain, the loop phase distribution, and the oscillation frequency of the loop.